The Dark Demise of T-Rex

By Tara Shears

The title makes it sound like a low-budget afternoon B-movie of the sort that might feature a plastic T-rex and alien gloopy stuff, but in fact this is a serious book about how dark matter might have been responsible for one of the biggest mass extinctions of all time. Your inner five-year-old and inner geek are going to be thrilled.

The dinosaurs were wiped out millions of years ago when an object the size of a city crashed into the Earth. Lisa Randall, a theoretical physicist, thinks that the villain is dark matter. This is mysterious stuff that we can’t see because light doesn’t shine from it–hence the ‘dark’. It accounts for 85 percent of all matter in the universe. Billions of dark matter particles probably stream through us every second without us even noticing. In fact, we only know that dark matter is there at all because the universe doesn’t make sense without it; it is the glue that stops stars from flying off galaxies, that explains the shape of colliding galaxies formed in the first place.

Randall guides us through the Solar System, which contains not just planets but dwarf planets, planetoids, asteroid belts, meteorites and meteoroids, all surrounded by a huge ghostly Oort cloud of billions of icy chunks extending out almost a light year away from the sun.

And we learn about mass extinctions on Earth, which occur every 30 to 35 million years. There are many suggestions as to why they might happen–perhaps killer volcanoes, or Nemesis (a hypothesized partner star in our solar system that knocks the sun off kilter every so often). But in one case evidence points to a killer ten-mile-wide meteoroid, landing in Mexico and destroying 75 percent of life (and most of the dinosaurs) 66 million years ago.

It’s only in the last part of the book that these diverse strands are brought together. Randall works on theories of dark matter in which there is a dark face at work, a sort of ‘dark light’ that sticks some (but not all) dark matter together. If the theory is true, a corollary is that a thin layer of sticky dark matter could lie inside our galaxy and cause problems. As the sun rotates around the galaxy, it bounces up and down through the dark matter, which can dislodge a meteoroid in the Oort cloud–every 30 to 35 million years pinging one off to Earth to wipe out whatever life exists.

Worried? Don’t be–the next impact isn’t due for millions of years, and Randall points out that the theory is unproven and that we’re more likely to cause extinction ourselves.

Randall is a great explainer. She writes clearly and precisely and entertains with analogies and stories. I particularly liked her use of George Clooney to illustrate dark matter’s influence, and her largely unnoticed appearance on the sitcom The Big Bang Theory to make a point about our powers of observation.

But perhaps the most interesting feature of this book is the way in which it shows how science progresses; through a bumpy journey of observations, hypotheses, re-evaluations, via leaps into the unknown, overseen with sometimes prejudicial guiding principles.

It’s not an easy read–it will stretch your mind and then some (it stretched mine and I’m a particle physicist), and you’ll need patience to get to the punch line. It will be enjoyed by those who want to learn more about the frontiers of the unknown or who like the idea of a cosmic murder mystery–and probably by some who just can’t resist the title.